The present invention relates to devices that dispense a volatile air treatment chemical by heating a substrate impregnated with, or coated with, the chemical. More particularly it relates to indicators used with such devices to indicate when the treatment chemical has been used up.
Substrates (particularly porous substrates) have previously been used as carriers for air treatment chemicals such as insect control agents (insecticides, insect repellents, insect growth regulators, insect attractants, synergists, etc.), fragrances and deodorizers. See e.g. U.S. Pat. Nos. 5,111,477; 5,647,052 and 6,663,838. The disclosure of these patents, and of all other patents referred to herein, are incorporated by reference as if fully set forth herein.
Upon heating the substrate a volatile air treatment chemical is caused to be dispensed from the substrate. The heating source is typically an electrical heater, but may instead be a flame.
A variety of air treating functions can be achieved with such devices. For example, a porous substrate impregnated with volatile insecticide can be used to prevent mosquito biting in a confined bedroom. Alternatively, a deodorizing or desired odor or odor control material can be dispensed to overcome malodors or to provide a desired fragrance.
A disadvantage associated with such devices is that the consumer may not be aware of when the substrate has been exhausted. Unlike systems that have a wick extending into a visible reservoir, substrate-type systems often do not visibly change significantly as the active chemical is dispensed.
While it is possible to include a suggested useful life on the packaging for such products, consumers may not read or remember that information. Further, given the wide range of heater performance to which such substrates may be exposed, providing suggested useful life information may not be accurate. This can lead to use of the substrate after its effective useful life (with resulting consumer dissatisfaction). Alternatively, it can lead to premature disposal of a still useful substrate (and thus unnecessary cost and waste).
Hence, there have been efforts to better inform consumers regarding the extent of use-up of such substrates. Some such efforts use a chemical indicator that undergoes a visual change as the substrate is heated. See e.g. U.S. Pat. No. 4,128,508 (evaporation of an air treatment chemical causes a pH change and thus a color change); U.S. Pat. No. 4,824,917 (evaporation of a solvent leads to a color change); and U.S. Pat. No. 6,790,670 (evaporation of a dye leads to a color change).
However, this typically involved mixing a chemical needed for the indicator to work directly with the air treatment chemical. Care therefore needed to be taken to avoid selecting incompatible chemicals. Also, an indicator chemical could affect the volatization properties of the air treatment chemical. Further, coordinating the visual cue provided by the volatization of the indicator chemical with the rate of use of the air treatment chemical was difficult, particularly because both the indicator and the treatment chemical were being exposed to similar conditions, even though they might have different dispensing properties.
In U.S. Pat. Nos. 5,647,502 (limited duration bulb) and 6,663,838 (consumable candle) there was some discussion of coordinating the disappearance or destruction of a separate mechanical element with the useful life of the air treatment chemical. For example, when a candle that was one such heating device was used up, that also provided an indication that the substrate needed to be replaced. However, the candle system is not applicable to non-flame environments, and the use of limited duration bulbs can be relatively expensive.
In U.S. Pat. No. 4,921,636 there was a further teaching of a separately manufactured visual indicator that could be associated with an air treatment product. However, structures for using this concept were not described in detail in this patent, nor were ways of creating a joint replaceable cartridge using these features, nor were ways of positioning the indicator at a different distance from the heater than the air treatment chemical, nor were ways of providing additional air treatment functionality.
Thus, a need exists for improved air treatment devices with an automatic use-up indicator.